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Flashcards in General Bacteriology Deck (32)
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Name the two mechanisms by which bacteria produce disease.

Invasiveness and toxigenicity.


Define virulence.

The degree of pathogenicity of a microorganism.


Name several bacterial virulence factors.

Capsules, toxins, enzymes, cell wall receptors, and pili.


How do capsules contribute to the virulence of certain bacteria?

They enable the organism to resist phagocytosis.


Compare endotoxins and exotoxins.



What is toxoid?

A toxin treated to decrease its toxicity but retain its antigenicity. It is given to stimulate anti-toxin production. The tetanus toxoid is an example.


What is an antitoxin?

An antibody against a toxin. Antitoxins are used to treat diseases caused by toxins, for example, botulism.


What kind of immunization results when a person is injected with a toxoid?

Artificially acquired active immunity.


What is an opportunistic pathogen?

An organism that does not cause harm in a healthy host, but which can cause disease in a debilitated or immunocompromised host.


What are some factors that can render an individual susceptible to opportunistic infections?

Very young or very old age, immune deficiencies, burns, dialysis, diabetes, chronic diseases, alcoholism, radiation, chemotherapy, organ transplants, invasive medical techniques, and antibiotics.


What is a commercial organism?

One that lives on or in the host without causing harm, for example, the normal flora of the skin, mouth, and GI tract.


What is a nosocomial infection?

An infection acquired while in the hospital.


Define zoonosis.

An infectious disease contracted from direct or indirect animal contact.


How do bacteria reproduce?

By binary fission. The cell divides into two genetically identical cells.


What is generation time?

The time it takes for a population to double. This varies from approximately 15 minutes for E. coli to 24 hours for Mycobacterium tuberculosis.


What is a facultative anaerobe?

An organism that can grow with or without oxygen. Most pathogen are facultative anaerobes.


What is an obligate anaerobe?

An organism that can not grow in the presence of oxygen, for example, Clostridium and Bacteroides. Moderately obligate anaerobes can tolerate some expose to oxygen but require an oxygen-free environment for growth. Strict obligate anaerobes are killed by even a few minutes of exposure to oxygen, so they require special handling to protect them from oxygen.


What is the optimum atmosphere for strict anaerobes?

80-85% nitrogen, 10% hydrogen, 5-10% carbon dioxide, and less than 1% oxygen.


What is a capnophilic organism?

An organism that requires increased carbon dioxide, for example, pathogenic Neisseria.


What concentration of CO2 is achieved with a candle jar?

Approximately 3%. This concentration is not sufficient for some capnophilic organisms such as Campylobacter. A CO2 incubator can be used to provide a concentration of 5-10% and commercial bio-bags are available for incubation of small numbers of plates.


What quality control is required for the CO2 incubator?

The CO2 concentration and temperature should be checked daily.


What types of candles should be used in a candle jar and why?

White unscented. Others may emit substances toxic to bacteria.


Which type of organisms will grow in a candle jar?

Aerobes, facultative anaerobes, and capnophilic organisms. The candle jar is not oxygen free.


What is a microaerophilic (microaerobic) organism?

An organism that requires a reduced level of oxygen in order to grow, for example, Campylobacter.


What is the usual temperature of incubation for bacterial cultures?

35-37C. Most human pathogens are mesophiles and grow best close to body temperature.


Name two organisms that grow at 42C?

Campylobacter and Pseudomonas aeruginosa.


Name two bacteria that can grow below 35C?

Listeria monocytogenes and Yersinia enterocolitica can grow from 0-40C. Cold enrichment may be used to enhance the recovery of these organisms.


What is the usual incubation time for bacterial cultures?

Most bacteria routinely encountered grow in 24-48 hours. Mycobacteria and some anaerobes require longer incubation.


What are molecular diagnostic techniques?

Techniques in which specific sequences of DNA or RNA are targeted for analysis. These methods allow for detection of microorganisms directly in the clinical specimen.


What are nucleic acid probes?

Probes are labeled single-strand sequence of DNA or RNA that are complementary to the nucleic acid sequence to be detected.